This invention relates generally to tankers for carriage of liquids such as oil and, more particularly, to a system for control of oil leakage from a damaged tanker. In a more specific sense, the invention relates to improvements to the oil leakage control system described in applicant's U.S. Pat. No. 4,964,437 dated Oct. 23, 1990 and copending U.S. patent application Ser. No. 07/728,200, filed Jul. 10, 1991.
Briefly, the system described in the patent minimizes the outflow of oil from a damaged cargo tank of an oil tanker of the "segregated ballast" type by transferring oil out of the upper part of the damaged cargo tank and at the same time, keeping to a minimum the reduction of draft at the damaged area. This is accomplished by valves and piping installed through selected bulkheads for connecting each cargo tank to one or more ballast tanks, one or more of the valves being opened upon occurrence of damage sufficient to cause cargo tank leakage, allowing oil to flow, by gravity, from the upper part of the damaged cargo tank or tanks to one or more ballast tanks which, if the tanker were loaded, would be empty. Each connection between a cargo tank and a ballast tank includes two valves, either butterfly or sluice valves, connected in tandem, to prevent oil contamination of ballast as any occur from valve leakage in normal operation. The valves typically have a diameter in the range from three to five feet, the choice being a trade-off between the cost of the valves and the rate at which it is desired to transfer oil from the damaged cargo tank to the ballast tank(s), and each is equipped with an actuator for opening and closing the valve. Considering that a typical tanker may require at least ten such pairs of valves to effectively control oil leakage by this method, the installation obviously is expensive.
A less expensive and more effective valve structure for use in the system described in applicant's copending application Ser. No. 07/728,200 filed Jul. 10, 1991, comprises a section of pipe installed in a bulkhead common to a cargo tank and a ballast tank which is normally closed at the ballast tank end by a one-shot valve including a blank flange bolted to an annular flange secured to the end of the pipe and a high pressure hydraulic hose compressed between the flanges and operative when pressurized to break the bolts and thereby release the flange. Upon occurrence of damage sufficient to cause cargo tank leakage, an instrumentation and control system applies hydraulic pressure to appropriate hydraulic hoses, thereby to open one or more passageways to allow oil to flow, by gravity, from the upper part of the damaged cargo tank or tanks to one or more ballast tanks.
Although this one-shot valve operates satisfactorily, it is relatively expensive to fabricate and install because of the need to drill a large number of bolt holes through two steel flanges, each of which may be three-fourths to one inch thick.
It is the primary object of the present invention to provide an improved one-shot valve adapted to be fitted in a bulkhead of a tanker and adapted to be opened in response to applied hydraulic pressure.
Another object of the invention is to provide a one-shot valve for initiating oil flow from a damaged cargo tank to a ballast tank which is more effective for the purpose, and less expensive, than the one-shot valve described in the forementioned copending application.